The Taiwan Patent Publication Nos. 140531, 160174, 173030, and 192038 disclose a catalytic converter, which is shown in FIG. 1 and is composed of an inlet 11, an expansion chamber 12, an outlet 13, and a reactor 14 covered with catalyst. In order to avert any adverse impact that the reactor 14 might have on the performance of the internal combustion engine, the catalytic converter is provided with the expansion chamber 12 for reducing the exhaust back pressure of the engine in operation. In the process, the exhaust fume is allowed to enter the expansion chamber 12 via the inlet 11 such that the flow of the exhaust gas passing the central area of the reactor 14 is greater than the flow of the exhaust gas passing the peripheral area of the reactor 14. As a result, the catalyst located in the central area of the reactor 14 is subjected to a more intensive chemical reaction with the exhaust fume, thereby resulting in an acceleration in the breakdown of the central area catalyst. On the other hand, the catalyst located in the peripheral area of the reactor 14 is relatively intact. It is therefore readily apparent that the prior art catalytic converter described above is inefficient at best, and that an improvement is called for.